A digital X-ray sensor having a two-dimensional detection plane is used for a medical X-ray imaging apparatus. There are various imaging modes in X-ray imaging such as computed tomography (CT) imaging, panoramic imaging (imaging of entire jaws), cephalometric imaging (head normalization photographing) and dental imaging (imaging of one or a few teeth in a small irradiation field). A digital sensor is developed to have an appropriate size and performance for each of the imaging modes. It is desirable that one X-ray imaging apparatus can be used in a plurality of modes. For example, in a digital X-ray imaging apparatus disclosed in JP-A H8-257,026/1996, an X-ray MOS sensor is used for panoramic tomography or linear tomography. Slit plates are provided for an X-ray source and for an X-ray MOS sensor, and the sizes of the openings of the slits are controlled according to an imaging mode among the panoramic tomography and linear tomography, and a range of pixels to be read in the MOS sensor is changed. An X-ray imaging apparatus disclosed in JP-A H10-225,455/1998 can change an imaging mode between computed tomography mode and panoramic tomography mode. Slit plates are provided for an X-ray source and for an X-ray MOS sensor, and the sizes of the openings of the slits are controlled according to an imaging mode among computed tomography and panoramic tomography modes.
However, in the X-ray imaging apparatus disclosed in JP-A H10-225,455/1998 for two imaging modes, a detection area in the digital X-ray sensor necessary for panoramic imaging is smaller than that for computed tomography imaging. Therefore, if the same digital X-ray sensor is used both for computed tomography imaging and for panoramic imaging, data are read out from pixel not needed to be read, so that excess data are transferred and stored, and a time therefor is wasted. Further, exposure to X-ray radiation is increased unnecessarily in proportion to the area in the two-dimensional detection plane. Therefore it is generally desirable that the digital X-ray sensor can be used efficiently for each imaging mode. It is described on the digital X-ray imaging apparatus disclosed in JP-A H8-257,026 having two imaging modes that the slits are changed according to the imaging mode, but it is not described to change an area for reading data or a time for reading data according to imaging mode in contrast to the embodiments of the invention to be explained later.